| Stress Evolution in Sol-Gel-Derived Thin Films |
| Hiromitsu KOZUKA |
| Kansai University |
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The residual stress in sol-gel-derived ceramic thin films greatly affects their properties and functionalities, results in bending of substrates, and hence is an important factor to be controlled. The stress is often thought to develop just as a result of the difference in thermal expansion coefficient between the film and the substrate. However, this is not correct. One should recognize that gel films are densified during heating under constrained conditions, where tensile strain is accumulated in in-plane direction, resulting in the development of in-plane tensile stress. A variety of processing parameters could affect the densification behavior, and hence could affect the evolution of stress during heating as well. During cooling after firing, on the other hand, thermal stress due to the difference in thermal expansion coefficient could be generated. Based on in-plane stress measurements, first we will demonstrate how the stress evolution during heating is affected by processing parameters. Second we will show how the heat treatment temperature could affect the residual in-plane stress. Although the residual stress exhibited a rather complex dependence on heat treatment temperature, the dependence could be understood in terms of film densification, structural relaxation, atomic diffusion, progress of crystallization and thermal strain.
References:
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[2] H. Kozuka, in Handbook of Sol-Gel Science and Technology: Processing, Characterization and Applications, Volume 1, "Sol-Gel Processing," edited by S. Sakka, Kluwer Academic Publishers, Norwell, U.S.A., 2005, pp. 247-287.
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[7] K. Ohno, H. Uchiyama, H. Kozuka, J. Appl. Phys.,.111, 014901 (2012).
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